Compositions are used extensively in a wide range of biomedical applications, for the delivery of diagnostic or therapeutic active agents. A longstanding problem in the manufacture of such compositions is the controlled delivery of the active agents to particular organisms or sites within organisms, such as a particular cell type. The timed release of active agents from such compositions, also remains problematic. These problems reside in part due to the manner in which such active agents are released from the composition.
Polymers may be cross-linked to form compositions that serve as a matrix or reservoir for delivery of a drug over a sustained period. For example, cross-linked hydrogels of polyacrylamide, are capable of absorbing a substantial amount of water to form elastic or inelastic compositions. The compositions may absorb water and swell to thereby release the drug incorporated therein. Unfortunately, the hydrogels may have a number of undesirable characteristics.
For example, some such compositions are not biodegradable. Therefore, the removal of the compositions from an organism requires excretion of the composition. Other compositions require the use of undesirable solvents or monomers during manufacture. For instance, a conventional manufacture of polyacrylamide uses the monomer acrylamide and cross-linker N,N′methylbisacryamide. Residual amounts of the unreacted monomer and cross-linker typically remain in the final composition and can cause damage in surrounding tissues or inactivation of the active agent incorporated into the composition. Moreover, the preparation of such compositions may preclude inclusion of the active agent during formation of the matrix. For example, the conventional preparation of a polyacrylamide gel involves formation of a free radical on the growing polymer chain and cross-linking chains. Such a process could chemically alter and inactivate an active agent present during the gel's formation. Therefore, additional processing steps are typically taken to first prepare a capsule and then add the active agent to the capsule, usually along with waxes, fats or other fillers, to help the capsule maintain its shape. Furthermore, because the release of the active agent from certain gels is governed by diffusion, release is not targeted to a particular area of the body of an organism.
Accordingly, one objective of the invention is a process for making a composition capable of forming a gel in the presence of an active agent without deleteriously effecting the active agent. Another objective of the invention is a composition that enables a targeted release of an active agent included therein.